The procedures for filtering samples for analysis of trace-organic compounds,
including volatile organic compounds, pesticides, and base-neutral compounds,
are summarized from Sandstrom (1995). CH/DH techniques and associated QA procedures
for inorganic analytes with parts-per-billion concentrations are not required
for organic analytes but are recommended as good field practices to maintain
the integrity of sample chemistry. Field personnel must wear disposable, powderless
gloves (gloves). These gloves must be able to withstand any solvents or other
chemicals that will be used during sample processing and equipment cleaning.
Equipment and supplies used to filter different types of organic compounds are
described in NFM 2. Additional information about organic-compound filtration
can be found in Ward and Harr (1990), Manning and others (1994), Shelton (1994),
and Koterba and others (1995).

5.2.2.A PLATE-FILTER PROCEDURE

Read through the procedures described in Sandstrom (1995) and presented in
tables 5-4 and 5-5 and in figure 5-1. Obtain the equipment needed (table 5-5),
test equipment operation, and collect an equipment blank if needed. Filtering
samples for organic-compound analysis inside a processing chamber and using
Clean Hands (CH)/Dirty Hands (DH) techniques is not mandatory but is recommended.

To filter sample for analysis of general trace-organic compounds in
solution:

CH: Load the filter onto the plate-filter assembly
within the processing chamber.

a.

Open precleaned plate-filter assembly.

b.

Place one stainless steel support screen on the base of the
plate-filter assembly--Use stainless steel forceps.

c.

Place one clean 0.7-µm pore-size glass microfiber filter
on top of the screen. Do not touch the filter
with fingers; use stainless steel forceps.

d.

Wet the filter with a few drops of pesticide-grade blank
water (PBW) from a fluorocarbon polymer wash bottle to help keep the filter
in place as the unit is assembled.

e.

Close plate-filter assembly--Align top and bottom plates.
Lightly tighten the locking bolts or locking ring. Attach a short
length of fluorocarbon polymer tubing to the outlet of the plate-filter
assembly to channel filtrate to a toss bottle, sink funnel, or drain.

f.

Add 10 to 20 mL of PBW rinse water through the
inlet in the upper plate to wet the filter completely before tightening
the clamps. (This rinse also helps prevent damage to the filter: a dry filter
might rupture when the plate-filter assembly is tightened.)

g.

Tighten the locking bolts or ring by hand. Overtightening
can cause the plate-filter assembly to
warp and leak and the filter to
rupture.

3.

CH/DH: Rinse the pump tubing (from a metering pump)
or the sample tubing (from a submersible ground-water pump) with the water
to be sampled. Discard rinse water into a sink funnel or toss bottle.

4.

Set up the pump for filtration.

•

CH: If using a metering pump, place intake end of tubing into
the container holding the sample. Attach discharge end of pump tubing
to the inlet connector of the plate-filter assembly. Use a stainless steel
compression fitting of the appropriate size to secure the discharge hose
to the inlet connector.

•

CH: If using a submersible pump, attach discharge end
of the sample tubing from the pump to the plate-filter assembly, keeping
tubing as short as practical. Use a stainless steel compression fitting
of the appropriate size to secure the discharge hose to the inlet connector.

5.

CH: Rinse and condition the filter. The total volume
of sample passed through the filter, including rinse water, needs to be
accurately determined to ±1 mL and recorded in the field notes.

a.

Turn on the metering pump at low speed or open the sample
tubing from the submersible pump and operate at a low flow rate.

b.

Open the air-vent valve located on top of the plate-filter
assembly. Tilt the assembly slightly to the side to allow all trapped air
to escape (vent).

c.

Close the air-vent valve when water discharges through the
valve.

d.

Pass 100 mL of sample through the filter to remove any residual
liquids from the cleaning or prewetting procedures. If concentration of
organic compounds in suspended-material phase is to be determined:

i.

Be sure that only one filter is transferred from its original container
directly to the plate of the filter assembly. Take care not to transfer
the paper liner that separates each filter.

ii.

The filter should never be removed from the original container
until each is transferred to the plate-filter assembly for use. (Exception:
polycarbonate (Nuclepore) filter medium is precleaned with acid solution.
If transferring one of these, hold the filter with forceps and rinse off
acid with inorganic blank water (IBW) dispensed from wash bottle.)

e.

Discard rinse water to a sink funnel or toss bottle.

6.

DH: Tare the weight of a clean, baked, glass sample
bottle. (First check to see if this is required for the analytical procedures
to be used.)

a.

Set up, level, zero, and check the accuracy of the balance
with a reference weight. Record accuracy in field notes.

b.

Tare the weight of a dry, clean, capped 1-L amber bottle,
and record the weight. Remove the bottle cap.

c.

Close the air-vent valve when water discharges through the
valve.

d.

Pass 100 mL of sample through the filter to remove any residual
liquids from the cleaning or prewetting procedures. If concentration of
organic compounds in suspended-material phase is to be determined:

7.

Filter and weigh each sample. (Do not field rinse baked, glass
sample bottles.)

a.

CH: Resume the flow of sample through the plate-filter
assembly.

b.

CH: Place the appropriate sample bottle under the
outlet of the plate-filter assembly.

c.

CH: Collect approximately 1 L of filtered sample for
each analytical schedule, but leave headspace in each bottle. If the filter
medium becomes too clogged to proceed, go to step 13 below.

d.

DH: Cap the bottle(s) and pass sample(s) out of chamber.
Wipe the bottle dry with a lint-free laboratory tissue, such as KimwipeTM,
to remove any condensation from the outside of the sample bottle.

e.

DH: Weigh and record the amount of sample filtered
(total weight minus tare weight of bottle).

f.

Chill samples immediately and maintain at or
below 4°C without freezing for shipment to the laboratory (section 5.5).

8.

CH: Remove as much water as possible from the inside
of the plate-filter assembly by using the metering pump to pump air through
the sample tubing, or by pulling water out through the outlet nozzle with
a peristaltic pump, or by using a syringe to apply positive air pressure
to the inlet connector. This removes any residual sample and prevents spilling
the water-sediment slurry when the plate-filter assembly is disassembled.

9.

CH: If sediment collected on the filter is to be analyzed
for organic compounds:

a.

Carefully disassemble the top of the plate-filter assembly.

b.

Using metal forceps, carefully fold the filter in half and
then in half again (quarters).

c.

Transfer the filter to a baked, wide-mouth glass jar with
a fluorocarbon-polymer-lined cap.

d.

Record on the jar label and on field forms the total volume
of sample that passed through the filter.

e.

Chill and maintain the sediment sample at or below 4°C
for shipment to the laboratory (section 5.5)

f.

Chill samples immediately and maintain at or
below 4°C without freezing for shipment to the laboratory (section 5.5).

10.

DH/CH: If sediment on the filter will not be analyzed,
disassemble the top of the plate-filter assembly and remove the filter with
forceps. Discard the filter appropriately. Rinse the plate-filter assembly
components and tubing immediately after the filter has been removed.

11.

DH/CH: If the equipment is
to be used at a subsequent site,
field clean all equipment while equipment
is still wet and before going
to the next site. Clean with detergent solution,
rinse with DIW, and final rinse with methanol--do not use methanol on equipment
used for TOC, DOC, or SOC samples (NFM 3). If the plate-filter assembly
will not be reused before returning to the office, rinse all components
with DIW. Put rinsed components and tubing in a resealable bag for cleaning
at the office laboratory.

12.

Document on field forms and in field notes the
filtration procedures used.

13.

If the filter medium
becomes clogged before the required volume
of sample has been collected, stop
the metering pump or divert the sample flow from the submersible pump (see
TECHNICAL NOTE below) and replace the filter with a new filter as indicated
in steps a through f below.

TECHNICAL NOTE: Diverting the flow of
sample being pumped with a submersible pump by use of a three-way valve
can result in a temporary increase in turbidity (NFM 4). Allow turbidity
to clear after reestablishing flow through the sample tubing and to the
plate-filter assembly.

a.

Remove as much water as possible from inside the plate-filter
assembly. The stainless-steel or aluminum plate-filter assembly does not
have an upper support screen, so the filter cannot be backflushed. Remove
the inlet tubing to the metering pump from the sample and either attach
tubing from a peristaltic pump to the outlet and pull residual water out,
or use a syringe to apply positive air pressure to the inlet connector.

b.

Remove the clogged filter with forceps. If sediment
collected on a filter is to be
analyzed for organic compounds, follow
directions in step 9.

c.

Load the plate-filter assembly with a new filter and reassemble
the unit as described in step 2.

d.

Prepare the filter as described in steps 2f and 5a-d, allowing
the first 125 mL of sample to remove any sediment particles that may have
moved below the filter during the replacement procedure. Use a graduated
cylinder to measure volume.

e.

Record the volume of sample rinsed through the plate-filter
assembly if sediment collected on the filter is to be analyzed for organic
compounds. Volume accuracy should be ±1 mL.

f.

Place a tared sample bottle under the plate-filter
assembly outlet, resume the flow of sample through the filter, and continue
to collect the sample filtrate.

The capsule-filter procedure for filtering samples for organonitrogen-herbicide
analysis described below is provided if the option to process these samples
onsite is selected. The steps that follow are taken from Sandstrom (1995), which
includes more detailed instructions and description of the equipment, including
the 25-mm diameter disposable nylon-media filter capsule (nylon filter):

1.

Before leaving for the field site, clean the nylon filter.

a.

Put on appropriate, disposable, powderless gloves (gloves).

b.

Place intake end of the metering pump tubing into the methanol.

c.

Pump about 10 mL through the nylon filter to a used-methanol
disposal container.

CAUTION: Do the following if using
methanol or other organic solvent:

Work under a fume hood or in
a well-ventilated area, NOT in the field vehicle.

Wear protection against skin
and eye contact and do not inhale fumes.

Collect
methanol rinse waste into proper disposal containers and dispose
of according to local regulations.

2.

At the field site, cover the field bench or table with a sheet
of aluminum foil or TeflonTM to prepare a clean work surface.

3.

Place equipment and supplies on the clean work surface. Remove
foil or other wrapping from precleaned equipment. Change gloves.

4.

Remove the nylon filter from the plastic bag.
Rinse the discharge end of the pump tubing with methanol. Discard used methanol
to a proper waste container. Attach the metering-pump tubing to the capsule
inlet; keep tubing as short as possible.

5.

If filtering with a metering pump, transfer the intake end
of the pump tubing to the sample. If using a submersible pump to collect
the ground-water sample, redirect the sample flow to and from the nylon
filter as needed, using a manifold flow-valve system.

6.

Purge air from the sample tubing. Before connecting the nylon
filter, allow ground-water sample to flow through the tubing at a very low
rate. This will require just a few milliliters of sample if a metering pump
is used. With sample flowing, connect tubing to the nylon filter. (Use a
LuerTM connector of appropriate size to secure the discharge
hose to the inlet connector.)

7.

Collect at least 100 mL of filtrate in a 125-mL baked amber
glass sample bottle. Do not completely fill the bottle. Allow 2-3 cm of
headspace. The headspace leaves space for matrix spike standards to be added
(if required) and prevents sample loss if the sample freezes.

8.

If the nylon filter medium becomes clogged before a sufficient
amount of sample has been filtered, replace it with a new nylon filter and
repeat steps 6 and 7 until at least 100 mL have been collected.

9.

When filtering is complete, cap the bottle firmly. Chill and
maintain the sample at or below 4°C without freezing during storage
and shipment to the laboratory (section 5.5).

10.

Discard the nylon filter. Field clean the pump and tubing
as described in NFM 3 before using the equipment at the next site.

11.

Document on field forms and in field notes the filtration
procedures used.

The standard filtration procedures for samples for analysis of dissolved organic
carbon (DOC samples) and suspended organic carbon (SOC samples) use 47-mm-diameter,
0.45-µm pore-size, silver-metal filter media. A gas-pressurized filter
assembly (SOC/DOC filter apparatus) constructed of either stainless steel or
fluorocarbon polymer is required (NFM 2). In addition, either a peristaltic
pump, a hand-air pump, or compressed gas (usually organic-free nitrogen gas)
is used to pressurize the SOC/DOC filter apparatus and force the sample through
the silver filter. Filtration procedures are identical for ground-water and
surface-water samples.

A different set of procedures and separate silver filters are used to process
the SOC and the DOC samples, unless suspended-material concentrations are low
(up to about 30 mg/L). This section describes methods for (1) filtration of
SOC samples only, (2) combined SOC/DOC sample filtration, and (3) filtration
of DOC samples only.

If sample contains a large
amount of suspended materials, at least
two filtrations must be performed: one
for SOC and one for DOC.

If sample contains low concentrations of suspended
materials, filtration procedures can be combined using the same silver filter.

Unless the study plan dictates an additional sample for quality
control, only one silver filter should be needed for the SOC filtration.

--

The SOC filtration requires a minimum of 0.5 mg of suspended
material in the 125-mL sample.

--

If filter clogging is a problem, or if it is difficult to
obtain the 125-mL volume of sample needed for the SOC analysis, 64 mL of
sample or multiple 64-mL samples can be substituted.

Immediately after each use, rinse the filter apparatus several
times with organic-grade DIW.

--

Field clean the filter apparatus while still wet if it is
to be used at the next site. Otherwise, rinse, bag, and return the apparatus
to the office laboratory for cleaning.

--

Thoroughly rinse the white (fluorocarbon polymer) O-ring and
any other fluorocarbon polymer parts.

--

After cleaning, double-wrap all apertures and the filter apparatus
with aluminum foil and place filter apparatus inside a sealable plastic
bag.

Blank water (VBW or PBW) from a freshly opened bottle should
be used for quality-control samples for the DOC analysis. This blank water
can also be used for prerinsing the silver filters. Once the bottle has
been opened, the VBW or PBW must not be used for collection of future quality-control
samples.

Document on field forms and in field
notes the filtration procedures used.

Do not use methanol or any other solvent to
clean SOC, DOC, or TOC equipment (NFM 3).

TECHNICAL NOTE: Use 64-mL or 125-mL baked
glass bottles (available from QWSU) instead of a graduated cylinder to measure
sample volume for the DOC or combined SOC/DOC analysis. The advantage of
using the baked glass bottles to measure volume is that they are certified
as clean, whereas graduated cylinders can be difficult to clean adequately,
especially under field conditions (Burkhardt and others, 1997).

•

Bottles for DOC samples must have been baked at 400°C and meet a
detection limit criterion for organic carbon of <0.1 mg/L detection
limit for DOC. Do not bake the graduated cylinder because calibration
will be lost.

•

Volumetric accuracy of the 125-mL and 64-mL baked glass bottles
is about ±1 mL.

SOC sample processing:

SOC analysis of the suspended material left on the silver filter requires
that the volume of sample passed through the silver filter be measured and recorded.
Determination of the volume of sample to be filtered for SOC analysis can depend
on the concentrations of suspended materials; however, the concentration of
humic and other substances that cause colored water, such as organic and inorganic
colloids, will affect the volume that can pass through the silver filter. The
sample volume that can pass through the silver filter decreases as the concentration
of suspended materials increases. A graph of the historical stream stage compared
to a graph of the suspended-material concentration will aid in estimating suspended-material
concentrations at a given surface-water site. Guidelines for selecting the volume
of sample to be filtered for SOC analysis, based on suspended-material concentrations,
are shown in table 5-6.

1.

Collect the SOC sample(s) in a baked glass bottle, either
at the centroid of the streamflow (NFM 4) or as a subsample from the churn
or cone splitter. The data-quality requirements of the study and site characteristics
determine where to withdraw the sample. If collecting sample at the centroid
of flow with a weighted-bottle sampler, fill the bottle to the top; this
is not necessary if subsampling from the churn or cone splitter. Cap the
bottle securely.

•

Use a 125-mL baked glass bottle for water with relatively small concentrations
of suspended materials (concentrations approximately less than 250 to
300 mg/L) ( table 5-6).

•

64-mL baked glass bottles are recommended for samples that
are colored or particulate laden.

•

A clean, graduated cylinder may be used when the volume of
sample to be filtered is less than 64 mL.

1.

Cover the bench or table with a sheet of aluminum foil to
make a clean work surface. Put on appropriate disposable, powderless gloves.
Assemble necessary equipment on the clean work surface.

a.

To remove airborne particulates, attach an in-line, 0.2-µm
pore-size filter (Acrodisc 50) to the inlet side of a dry pump hose
that goes to the filter apparatus when using peristaltic or hand pumps to
pressurize the apparatus.

b.

Change gloves.

c.

Remove the aluminum foil wrapping from equipment.

3.

Disassemble the clean filter apparatus.

4.

Using metal forceps, place a silver filter on the base of
the filter apparatus between the support screen and the fluorocarbon polymer
gasket, and screw the barrel onto the filter base. (There is no gasket in
the fluorocarbon polymer apparatus.)

5.

Pour a minimum of 100 mL of ASTM Type II reagent
water (Burkhardt and others, 1997) or VBW or PBW into the barrel. Analysis
of the water used must indicate less than 0.1 mg/L of organic carbon.

6.

Screw the top part of the filter apparatus onto
the barrel and attach a clean, dry hose, either from a peristaltic pump,
hand pump, or compressed gas cylinder (use a clean metal hose clamp to secure
the discharge hose to the inlet connector). Set the filter apparatus into
a stand.

7.

Apply pressure to start the flow of rinse water
through the filter apparatus, using either a peristaltic pump or hand pump,
or by regulating the flow of compressed gas (usually nitrogen).

Make sure that the pressure regulator
valve is closed. Turn the handle on the pressure
regulator counterclockwise for several turns until the pressure-regulator
valve is closed.

ii.

Open the valve to the nitrogen cylinder.

iii.

Open the pressure-regulator valve by turning the handle
clockwise until up to 15 lb/in2 registers
on the pressure
gage. Do not exceed 15 lb/in2 of pressure.

c.

Discard rinse water.

8.

Depressurize the filter apparatus. Always
point the apparatus away from your
body, face, and other people. When
using compressed gas,

a.

Close the valve to the pressure regulator after the pressure
gage shows no pressure.

b.

Close the valve to the gas cylinder.

c.

Change gloves.

Wear safety glasses when pressurizing or depressurizing
the filter apparatus.

9.

Remove the top of the filter apparatus carefully.

10.

Shake the sample vigorously (swirl if using a graduated cylinder)
to suspend all particulate matter. (This is possible even if the bottle
is filled to the top.)

11.

Pour an aliquot of the sample immediately into
the barrel of the filter apparatus, keeping particulates suspended.

12.

Screw the top part of the filter apparatus onto
the barrel and pressurize to filter the sample. Follow the instructions
in step 7 (above) for pressurizing the filter apparatus.

13.

After an aliquot of sample has been filtered
or filtrate is being collected at less than one drop per minute:

a.

Depressurize apparatus (step 8).

b.

Remove the top of the filter apparatus.

c.

Check if there is water on the silver filter and if it is
covered with particulates.

•

If the silver filter is dry but not covered with particulates, add another
aliquot of sample by repeating steps 10-12.

•

After the silver filter is dry and covered with particulates,
continue to step 14.

TECHNICAL NOTE:

It is important that all the water in the barrel be
passed through the silver filter, leaving the filter “dry.” To
accomplish this, it might be necessary to filter the sample as separate
aliquots, repeating steps 10-13 until the filter is loaded to capacity.

Shake the sample to resuspend particulates before pouring
each aliquot into the barrel.

If using a 125-mL or 64-mL bottle, it is not necessary
to empty the entire sample volume. Use of a clean, graduated cylinder
also is acceptable.

It is recommended (but not required) that the sides of
the barrel of the filter apparatus be rinsed with organic-grade DIW.

14.

Collect the filtrate in a 50-mL or other appropriately sized
graduated cylinder.

•

If additional aliquots will be filtered through the same silver filter,
collect all the filtrate in the graduated cylinder.

•

When the entire filtration is complete, record the total volume
of filtrate on field forms and on the Analytical Services Request (ASR)
form.

•

Discard filtrate in the graduated cylinder--Donot
send to laboratory for analysis.

15.

Depressurize (step 8) and disassemble the bottom
of the filter apparatus.

a.

Use a pair of metal forceps to remove the silver filter.

b.

Fold the silver filter in half with suspended material on
the inside, taking care not to lose any suspended material. Do not
wrap the silver filter in aluminum
foil.

c.

Place the folded silver filter into a petri dish for SOC analysis.

d.

Close the petri dish and label it with site identification,
date and time, total filtered volume of sample, and laboratory sample designation
code. (The total volume of filtered sample includes the volume used to precondition
the silver filter(s).)

e.

Maintain SOC sample at or below 4°C during storage and
shipment to the laboratory.

Combined SOC/DOC sample processing:

Procedures for a combined filtering of samples for SOC and DOC analysis are
listed below. Additional information can be found in Burkhardt and others (1997).

1.

Collect the sample for SOC/DOC analysis as instructed in NFM
4.

2.

Cover the bench or table with a sheet of aluminum foil to
make a clean work surface. Put on appropriate disposable, powderless gloves.
Assemble necessary equipment on the clean work surface.

a.

To remove airborne particulates, attach an in-line, 0.2-mm
pore-size filter (Acrodisc 50TM) to the inlet side of a dry pump
hose that goes to the filter apparatus when using peristaltic or hand pumps
to pressurize the apparatus.

b.

Change gloves.

c.

Remove the aluminum foil wrapping from equipment.

3.

Disassemble the clean filter apparatus.

4.

Using metal forceps, place a silver filter on the base of
the filter apparatus between the support screen and the fluorocarbon polymer
gasket, and screw the barrel onto the filter base. (There is no gasket in
the fluorocarbon polymer apparatus.)

5.

Pour a minimum of 100 mL of ASTM Type II reagent
water (Burkhardt and others, 1997) or VBW or PBW into the barrel. Analysis
of the water used must indicate less than 0.1 mg/L of organic carbon.

6.

Screw the top part of the filter apparatus onto
the barrel and attach a clean, dry hose, either from a peristaltic pump,
hand pump, or compressed gas cylinder (use a clean metal hose clamp to secure
the discharge hose to the inlet connector). Set the filter apparatus into
a stand.

7.

Apply pressure to start the flow of rinse water
through the filter apparatus, using either a peristaltic pump or hand pump,
or by regulating the flow of compressed gas (usually nitrogen).

Wear safety glasses when pressurizing or depressurizing
the filter apparatus.

Make sure that the pressure regulator
valve is closed. Turn the handle on the pressure
regulator counterclockwise for several turns until the pressure-regulator
valve is closed.

ii.

Open the valve to the nitrogen cylinder.

iii.

To pressurize the filter apparatus, open the presure-regulator valve by turning the handle clockwise until up to 15 lb/in2 registers
on the pressure
gage.

c.

Discard rinse water.

Do not exceed 15 lb/in2
of pressure.

8.

Depressurize the filter apparatus. Always
point the apparatus away from your
body, face, and other people. When
using compressed gas,

a.

Close the valve to the pressure regulator after the pressure
gage shows no pressure.

b.

Close the valve to the gas cylinder.

c.

Change gloves.

9.

Remove the top of the filter apparatus carefully.

10.

Condition the silver filter for the SOC/DOC sample:

a.

Select the volume of wholewater (either 64 mL or 125 mL)
to be filtered based on the estimated suspended-materials concentration
of the sample, and record the volume on the ASR and the field forms. The
volume to be filtered can be based on the table 5-6 guidelines and on previous
experience of filtering samples from the site.

b.

Shake the sample vigorously to resuspend settled particles
and measure the sample volume using a clean, baked 64-mL or 125-mL bottle
filled to the very top. Do not field rinse baked
glass bottles. Immediately transfer the entire volume
of the sample container to the barrel of the filter apparatus.

c.

Screw the top part of the filter apparatus onto the barrel
and pressurize to filter the sample. Follow the instructions in step 7 (above)
for pressurizing the filter apparatus.

d.

Condition the silver filter by passing 15 to 25 mL of sample
water through the filter to waste. (Pass 15 mL of sample water through the
silver filter if using a 64-mL volume of sample; 15 mL is the minimum volume
of sample that should be used.) Record the total volume of water that was
passed through the silver filter.

Do not field rinse DOC bottle.

11.

Place a 125-mL baked glass bottle under the discharge tube
of the filter apparatus and collect the sample filtrate for the DOC analysis
(100 mL is recommended; a minimum of 50 mL is required). If the silver filter
clogs before sufficient volume for the SOC analysis can be filtered, start
the process over and filter a smaller volume of water; the 64-mL bottles
are useful for such conditions. If the silver filter
clogs before the entire volume of
the 64-mL bottle can be filtered,
this combined SOC/DOC method cannot be
used. Start over and filter SOC
and DOC samples separately.

•

If the volume needed for the SOC analysis is insufficient for a DOC analysis
(less than 50 mL), two or more filtrations through separate silver filters
can be combined into one DOC bottle. (Retain two of the filters if a duplicate
SOC analysis is planned and record the total volume of sample that passed
through each of the retained filters.)

•

Each time a new silver filter is used, repeat steps 3-10,
rinsing and conditioning the silver filter as described. Discard the first
15 or 25 mL of sample filtrate to waste. Reposition the DOC bottle under
the discharge tube and collect the sample filtrate. Record the total volume
of sample that was passed through each silver filter.

•

If the volume needed for SOC analysis is greater than the
100 mL of sample to be used for DOC analysis, remove DOC bottle after filling
with 100 mL of filtrate, but continue filtering until the entire volume
needed for SOC analysis has been filtered. (Record total volume filtered
and discard extra filtrate.)

12.

After the DOC sample has been collected and the volume for
SOC analysis has been filtered, cap the DOC bottle securely and check that
the bottle is labeled correctly and completely. Place the bottle in a foam
sleeve before placing in an ice-filled shipping container.

13.

Depressurize the filter apparatus (step 8), then disconnect
the hose from the filter apparatus cylinder and remove the top. When depressurizing
the compressed-gas-operated apparatus:

a.

Close the valve to the pressure regulator only after the
gage indicates no pressure.

b.

Close the valve to the nitrogen cylinder.

14.

Using no more than a total of 20 mL of organic grade DIW:

•

Rinse residual suspended matter from the bottle that was used to measure
sample volume and pour into the filter barrel.

•

Rinse any residual suspended matter from the sides of the
filter barrel.

15.

Reconnect the top of the filter apparatus. Attach the pressure
hose and pressurize (step 7), passing the organic-grade DIW rinse water
through the silver filter. Discard rinse water to waste. Depressurize the
filter apparatus (step 8).

16.

Disassemble the bottom of the filter apparatus and remove
the silver filter.

a.

Use a pair of metal forceps when removing the silver filter.

b.

Fold the filter in half with suspended material
on the inside, taking care not to lose any suspended material. Do not
wrap the silver filter in aluminum
foil.

c.

Place the folded filter in a petri dish for SOC analysis.

d.

Close the petri dish and label dish with site identification,
date and time, total filtered volume of sample, and the laboratory sample
designation code. (Include the volume used to precondition the silver filter(s)
in the total volume of filtrate.)

e.

Place the labeled petri dish in a sealable plastic bag.

f.

Chill DOC and SOC samples and maintain at or below 4°C
without freezing (section 5.5). For SOC samples submitted to NWQL, record
the total volume of filtrate on the comment line of the ASR form.

g.

If more than one silver filter was needed for the SOC sample,
place each silver filter into a separate petri dish that is labeled as described
in step 16d. Place all the petri dishes for a single sample into one sealable
plastic bag labeled with the site identification and the date and time of
sample collection. This is submitted as a single sample.

•

Package the silver filter(s) for duplicate SOC analysis separately.

•

Ship samples for SOC analysis to the laboratory with a note
on the ASR form stating the number of silver filters used.

For SOC analysis, record TOTAL VOLUME of sample
that passed through each silver filter.

DOC sample processing:

Procedures for filtering a DOC-only sample are listed below. Additional information
can be found in Burkhardt and others (1997).

1.

Collect the sample for DOC analysis (NFM 4).

2.

Cover the bench or table with a sheet of aluminum foil to
make a clean work surface. Put on appropriate disposable, powderless gloves.
Assemble necessary equipment on the clean work surface.

a.

To remove airborne particulates, attach an in-line, 0.2-µm
pore-size filter (Acrodisc 50) to a dry pump hose in front
of the filter apparatus when using peristaltic or hand pumps to pressurize
the apparatus.

b.

Change gloves.

c.

Remove the aluminum foil wrapping from equipment.

3.

Disassemble the clean filter apparatus.

4.

Using metal forceps, place a silver filter on the base of
the filter apparatus between the support screen and the fluorocarbon polymer
gasket, and screw the barrel onto the filter base. (There is no gasket in
the fluorocarbon polymer pressure-filter apparatus.)

5.

Pour a minimum of 100 mL of ASTM Type II reagent
water (Burkhardt and others, 1997) or VBW or PBW into the barrel. Analysis
of the water used must indicate less than 0.1 mg/L of organic carbon.

6.

Screw the top part of the filter apparatus onto
the barrel and attach a clean, dry hose, either from a peristaltic pump,
hand pump, or compressed gas cylinder (use a clean metal hose clamp to secure
the discharge hose to the inlet connector). Set the filter apparatus into
a stand.

7.

Apply pressure to start the flow of rinse water
through the filter apparatus, using either a peristaltic pump or hand pump,
or by regulating the flow of compressed gas (usually nitrogen).

Wear safety glasses when pressurizing or depressurizing
the filter apparatus.

Make sure that the pressure regulator
valve is closed. Turn the handle on the pressure
regulator counterclockwise for several turns until the pressure-regulator
valve is closed.

ii.

Open the valve to the nitrogen cylinder.

iii.

Open the pressure-regulator valve by turning the handle
clockwise until up to 15 lb/in2 registers
on the pressure
gage. Do not exceed 15 lb/in2 of pressure.

c.

Discard rinse water.

8.

Depressurize the filter apparatus. Always
point the apparatus away from your
body, face, and other people. When
using compressed gas,

a.

Close the valve to the pressure regulator after the pressure
gage shows no pressure.

b.

Close the valve to the gas cylinder.

c.

Change gloves.

9.

Remove the top of the filter apparatus carefully.

10.

Condition the prerinsed silver filter:

a.

Open the barrel of the filter apparatus and pour about 125
mL of wholewater sample into the barrel (or about 64 mL if silver filter
media is expected to clog). For water with large concentrations of suspended
materials, collect the sample first into a baked glass bottle, allow suspended
materials to settle, and pour 125 mL of the clear supernatant into the filter
barrel.

b.

Screw the top part of the filter apparatus onto the barrel.

11.

Apply pressure to start the flow of sample through the filter
apparatus (step 7).

•

Do not exceed 15 lbs/in2.

•

If using compressed gas, open the pressure-regulator valve
first, then the valve to release gas from the cylinder (tank).

12.

Condition the silver filter media by passing about 25 mL of
sample through the silver filter to waste.

13.

Filter the sample:

a.

Place a 125-mL organic-free amber glass bottle under the
discharge tube of the filter apparatus. Do not prerinse
the DOC bottle.

b.

If the silver filter media clogs, depressurize the filter
apparatus and replace the silver filter.

i.

Rinse the new filter with blank water as described in steps 5-9.

ii.

Fill a clean DOC bottle with the water to be sampled and
let the suspended materials settle before decanting the sample into the
barrel of the filter apparatus.

iii.

Condition the new silver filter by passing about 25 mL of
sample through the filter to waste.

iv.

Reposition the DOC bottle under the discharge tube and continue to collect
the filtrate.

c.

Fill the bottle until sufficient volume for DOC analysis
has been collected (50 mL is the minimum requirement; 100 mL is recommended).
Cap the bottle securely and check that the bottle is labeled correctly.
Place the bottle in a foam sleeve before placing in an ice-filled shipping
container.

14.

Depressurize the filter apparatus (step 8).

15.

Chill and maintain the DOC sample at or below 4°C without
freezing (section 5.5).

16.

Disassemble the bottom of the filter apparatus. Remove the
silver filter with metal forceps and place the filter in a plastic bag for
disposal or recycling. Do not reuse silver filters.

Never increase the pressure in a filter apparatus
to greater than 15 lb/in2
in order to increase the rate of filtration.